Current evidence is limited to several small sample size, single and multi-agent phase I and II studies on biliary tract cancer, that subsumed gallbladder cancer together with various subtypes of cholangiocarcinoma and the majority of which did not include predictive testing of PD-L1 expression prior to treatment initiation [33,34,35,36,37,38]. The gene discussed is CD274; the disease is cholangiocarcinoma.